hi,
some hotfixes here about NAV 2009 SP1 & R2
support.microsoft.com/.../2618652
"The email message body is incorrect when you create an email message by using the AppendBody method in Microsoft Dynamics NAV 2009 Service Pack 1
•2280492
Attachments are not released until the Microsoft Dynamics NAV client is closed when you use the SMTP Mail codeunit (400) to send email messages that have attachments
•2516144
You receive malformed email messages if you use a specific version 7 release of the Microsoft.Navision.Mail.dll file in Microsoft Dynamics NAV 2009
try to use this hotfixes